Assuming you have a pool of accurately reported exchange volumes (not every exchange fakes volume), you can get a fairly good estimate for a site's volume based off its web traffic. Exchanges that have much higher volume than their web traffic suggests are consequently adjusted.
So liquidity can be faked but web traffic can't be done so easily?
Everything can be faked, we have fake yt,fv,tw profiles with thousands of web followers, how much do you think it will pump 100k visitors?
Besides, similarweb si a piece of garbage of its own when you go and get stats country by country you will see hilarious rankings, just take a look at Japan or Saudi Arabia., this is because they can only get data from the sources who are willing to tell them (and which can obviously be fake) and from users who install their extensions or app, which again is 1002% biased.
Yeah, liquidity can be gamed, but it comes with a lot of problems, you can't put fake walls continuously and either take hits during dumps or annoy customers that their trade orders haven't been executed or were so at 10% difference. You can fake activity when bots play for a billion 1 cent trade, but what will you do with a fake wall when somebody really wants to dump...take the hit or execute the trade till zero?
Web traffic overall numbers can be faked, but there are a bunch of obvious signs that this is the case. For example, take a look at Cointiger's web traffic analytics: https://www.rank2traffic.com/cointiger.com
72% of traffic is from paid referrals, resulting in an extremely high bounce rate of 85% and low engagement.
For legit exchanges like Binance, the numbers are much different: https://www.rank2traffic.com/binance.com
Almost no referral traffic and much higher engagement numbers.
Not a perfect metric by any means, but it is one of the few that cannot be completely manipulated. It is unfortunate that sites like Similarweb are off for some countries, but it is better than nothing.